The invention relates to a process and an apparatus for filling and/or rinsing an extracorporeal blood circuit.
Specifically, though not exclusively, the invention can be usefully applied for priming an extracorporeal circuit in a dialysis apparatus.
As is well-known, before performing a dialysis treatment, the extracorporeal blood circuit of the dialysis apparatus has to be filled with an isotonic fluid, normally a sodium chloride solution with a concentration of 155 mmol/l. This procedure, known as “priming”, has the aim of rinsing the circuit and removing the air and any particles and sterilising agents which might still be in the circuit.
With the aim of eliminating all of the air and filling with liquid both the blood side and the dialysis side of the dialyser, the prior art comprises a priming process in which the dialyser is first rinsed on one side, for example the dialysis side, from the bottom to the top; then it is upturned and rinsed on the other side.
Also known are various procedures which avoid the need to upturn the dialyser. One of these, used in the Seratron machine (Seratronics, Walnut Creek, Calif., USA) includes inverting the flow on the blood side of the dialyser. Other procedures include inverting the flow on the dialysis side by means of valves or pumps (see for example U.S. Pat. No. 4,324,662 and EP 0 366 950). EP 0 161 686 includes evacuating the air from the blood side by means of an aspiration unit in order to enable a following filling-up with the physiological solution. Finally, various methods are also known which include filling the blood side by backfiltering, i.e. forcing the liquid to transfer from the dialysis side to the blood side across the dialyser membrane.
Normally known priming procedures include, after the stage of complete filing of the extracorporeal circuit with the isotonic solution, a rinsing stage so that the isotonic solution in circulation is free of particles and sterilising agent. Finally the extracorporeal circuit is connected up to the patient: to do this the arterial line of the circuit is usually connected to the patient and the blood is made to enter the circuit by the blood pump, while the isotonic solution is sent to a discharge through the outlet of the venous line. When the blood arrives in proximity of the outlet of the venous line the blood pump is stopped to enable the venous line to be connected up to the patient. Alternatively the venous line is connected to the patient before activating the blood pump, so that the isotonic solution is infused into the patient and not discharged externally.
The process for filling the extracorporeal blood circuit according to the present invention is of the backfiltering type. There follow some descriptions of some known processes for filling via backfiltering.
DE 34 42 744 describes a process for re-use of a dialyser, according to which the used dialyser is first cleaned and disinfected, and then rinsed and tested. During the cleaning and disinfecting stage the dialyser is connected to the dialysis liquid circuit and to the extracorporeal blood circuit, as it is during a treatment, while the patient connection to the arterial line is connected to the fresh dialysis supply liquid and the patient connection line to the venous line is connected to the used dialysis liquid discharge line. A cleaning and disinfecting liquid is circulated along the fresh dialysis liquid supply line, then along the arterial line and then the venous line, and is finally discharged through the used dialysis liquid discharge line. During this stage, among other things, at least a small part of the cleaning and disinfecting liquid is forced to pass from the dialysis side of the dialyser to the blood side in backfilter through the membrane, in order to detach the layer of proteins that adheres to the blood side surface of the membrane. During the following rinsing stage, the patient connection to the arterial line is connected, by means of an adapter, to the patient connection to the venous line, so as to create a closed circuit; then the blood pump is set to operate continuously while the closed circuit is cyclically and repeatedly filled and emptied with water coming from the dialysis circuit, which is forced to pass through the dialyser membrane, alternatingly backfiltering and ultrafiltering. Then the water inside the blood circuit is dialyzed by the dialysis liquid flowing through the dialysis circuit.
A drawback of the process of DE 34 42 744 is that the rinsing stage is long, as an efficient rinse requires a passage of the liquid in both directions alternatingly for a considerable number of cycles. The rinse times are further lengthened because the passage of liquid through the membrane, both during the filling stage and the discharge stage, is by necessity relatively slow.
A further drawback of the process of DE 34 42 744 is that the rinsing action does not entirely purge the extracorporeal circuit of any particles remaining after the cleaning and disinfection stage which are bigger than the pores of the membrane.
A further drawback of the process of DE 34 42 744 is that the extracorporeal blood circuit is provided with a breather device that is relatively complex and expensive.
U.S. Pat. No. 5,259,961 describes some processes for rinsing, degassing and filling an extracorporeal blood circuit used in a dialysis apparatus.
In a first process described in U.S. Pat. No. 5,259,961, the dialyser is connected to the dialysis liquid circuit of the machine, as happens during a treatment; an end of the arterial line is connected, by means of an adapter, to the dialyser venous connection; the pump segment of the arterial line is connected to the blood pump; the other end of the arterial line is connected to an end of the venous line, while the other end of the venous line is connected, by means of a three-way valve, to the drainage line of the dialysis liquid discharging from the dialyser. The dialysis liquid prepared by the machine for dialysis is conveyed, by the blood pump, through the dialyser membrane (where it is filtered) into the arterial line and then to the venous line, then to return into the dialysis liquid circuit through the three-way valve.
This first process of U.S. Pat. No. 5,259,961 has, however, the drawback that various operations have to be performed after the circuit priming and before the dialysis treatment; the arterial line, for example, has to be detached from the venous connection of the dialyser and engaged to the arterial connection; further, the venous line has to be detached from the arterial line and engaged to the venous connection. This means not only more laborious activity for the operator, but also leads to a risk of circuit contamination.
In a second process described in U.S. Pat. No. 5,259,961, the arterial line and the venous line are connected, at an end thereof, to the respective arterial and venous connections of the dialyser, and at the opposite ends thereof to a valve arranged on the dialysis liquid circuit drainage line. The valve is commanded so as to prevent, totally or partially, the outflow from the dialysis chamber of the dialyser and to permit the drainage of the liquid from the arterial and venous lines towards the machine discharge. The dialysis liquid coming from the dialysis machine is forced, by the supply pump in the dialysis liquid circuit, to pass through the dialyser membrane into the venous and arterial lines, to perform the rinse and filling thereof, then to be discharged through the drainage line of the dialysis liquid circuit. Alternatively, the liquid used can be discharged into a further recipient.
A drawback of the second process of U.S. Pat. No. 5,259,961 derives from the presence of two ends (one on the venous line and the other on the arterial line) communicating with a discharge, with a consequently greater risk of contamination of the circuit with respect to the first process of U.S. Pat. No. 5,259,961, in which only one end (the venous end) communicates with the discharge.
EP 0 560 368 describes various processes for rinsing and filling an extracorporeal circuit of a dialysis machine, according to which the arterial line and the venous line are connected to the dialyser in the same way as during dialysis treatment, the pump segment of the arterial line is connected to the blood pump and the patient connection of the arterial line is connected to the patient connection of the venous line, in order to create a closed circuit. During the rinsing and filling of the extracorporeal circuit, the blood pump is activated to function in a reverse direction to normal functioning direction during dialysis treatment, thus generating a depression which aspirates the dialysis liquid, forcing it to pass through the dialyser membrane to enter the closed-circuit extracorporeal circuit. Furthermore, a service line connected to the upper part of the venous expansion chamber is connected to outside of the extracorporeal circuit in order to enable air to be expelled, together with excess liquid present in the circuit.
In a first process of EP 0 560 368, a valve closes the venous line between the venous expansion chamber and the dialyser, while the service line is connected to a collection container or to the machine dialysis liquid circuit. To intensify and complete the rinse of the whole closed circuit the valve between the venous chamber and the dialyser is repeatedly opened and at the same time another valve closes the service line; if required, the blood pump direction can be inverted in order to operate in the direction of normal use during treatment.
This first process of EP 0 560 368, however, has the drawback of considerable complication, due to the use of two closure valves (one on the venous line between the expansion chamber and the dialyser and the other on the venous service line connected to the discharge) which are added to the closure valve normally present on the venous line between the expansion chamber and the patient connection.
In a second process of EP 0 560 368, the valve for closing the venous line between the venous expansion chamber and the dialyser is no longer necessary, while the service line is placed in communication with an aspiration device, such as for example the degassing system of the dialysis machine, so that the rinsing liquid can circulate along the whole circuit formed by the extracorporeal circuit.
The second process of EP 0 560 368 is however affected by a considerable complication due to the use of as aspiration device which, even if present on the machine for other reasons, has to be adapted and commanded to perform a further function.
In a third process of EP 0 560 368, the service line is connected to the dialysis liquid supply line and is operatively associated to a reversible pump, i.e. a pump that can circulate liquid in both directions. The service line also exhibits a block valve, arranged between the reversible pump and the venous expansion chamber, and an elastic bag of about 20-50 ml volume, arranged between the reversible pump and the block valve to form a variable-volume chamber. During the rinsing and filling stages, the reversible pump operates as an aspiration device for expelling the excess air and the liquid. During the dialysis treatment, in which the block valve is always closed, the reversible pump periodically sends the liquid contained in the elastic bag to the dialysis side of the dialyser, to wash out the membrane by backfiltering, to detach the layer of proteins that deposits on the blood side of the membrane. The volume of cleaning liquid in the elastic bag is restored by inverting the operating direction of the reversible pump.
This third process too of EP 0 560 368 requires the use of a rather complex apparatus.
U.S. Pat. No. 6,132,616 describes a rinsing and filling process of an extracorporeal blood circuit in a dialysis apparatus, in which the rinsing liquid is forced to pass through the dialyser membrane from the dialysis side to the blood side. The arterial line and the venous line are connected to each other in such a way as to create a closed circuit. A three-way shunt valve, predisposed on the venous line in proximity of the patient connection end, enables drainage of the rinsing liquid from the blood circuit through a branch conduit communicating with one way of the shunt valve, on one side, and with a dialysis liquid preparation circuit on the other side. This stage lasts for a predetermined time, after which the blood pump recirculates, in a closed circuit, the rinsing liquid left in the circuit, while a dialysis liquid circulates in the dialysis compartment of the dialyser, until the ionic concentration of the liquid in the extracorporeal circuit reaches that of the dialysis liquid by means of diffusion through the membrane.
The process described in U.S. Pat. No. 6,132,616 is somewhat complicated, however, due to the presence of both a special intermediate point of connection of the extracorporeal circuit from which the branch conduit branches off, and because of a special three-way shunt valve predisposed in the above-mentioned intermediate point of connection in order to enable drainage of the extracorporeal circuit through the branch conduit.
U.S. Pat. No. 6,277,272 describes a process for priming and cleaning the extracorporeal blood circuit in a dialysis apparatus having a fluid balancing device, of a type comprising volumetric chambers. A pressurisation line is arranged in parallel to the fresh dialysis fluid supply line in order to bypass the volumetric chamber of the fresh dialysis liquid. According to the process of U.S. Pat. No. 6,277,272 the fresh dialysis liquid is forced to pass through the dialyser membrane in the extracorporeal circuit arranged on the pressurisation line. In a first stage the blood pump rotates in the inverse direction with respect to the normal blood circulation direction and the venous line closure valve is active, so that the dialysis fluid performs the priming and cleansing of the arterial line and then is discharged through the line itself. In a second stage, the occlusive blood pump is stopped and the valve on the venous line opened, while the pressurisation pump pushes the dialysis liquid through the membrane and thus along the venous line, towards the patient connection which functions as a discharge end.
A drawback of the process of U.S. Pat. No. 6,277,272 is its complexity, due to the use of a pressurisation line and pump. A further drawback is the presence of two connections with the discharge, which leads to a greater risk of contamination of the extracorporeal circuit.
EP 1457218 describes an automatic priming system of an extracorporeal circuit, by backfiltering through the dialyser membrane, comprising a reversible blood pump, an evacuation line connected to the top of the venous expansion chamber to eliminate excess liquid, a first clamp on the evacuation line, a second clamp on the venous line between the expansion chamber and the dialyser, a first pump on the supply line of the freshly dialyzed liquid to the dialyser, a bypass line with two ends connected to the drainage line to bypass the drainage pump, and an adjustment pump for the backfiltering rate arranged on the bypass line. EP 1457218 describes various priming processes of the extracorporeal circuit, according to which: the arterial line and the venous line are connected to the dialyser, as during the treatment, and are connected up to one another at the patient connections; the backfilter flow rate through the membrane of the dialyser is regulated by means of the regulation pump; and the flow rate of the excess liquid through the evacuation line is regulated in combination by the regulation pump and the blood pump, inversely activated.
EP 1457218 has however the drawback of having a certain constructive complexity, due to the predisposition of the bypass line and the regulation pump, together with the fact that at the end of the priming operation the venous expansion chamber liquid level has to be adjusted.
U.S. Pat. No. 5,863,421 describes a machine for dialysis which uses an automatic priming process of the dialyser membrane, in which a control unit activates the blood pump, the dialyzed liquid pump and two check valves (clamps), one on the arterial line and the other on the venous line, so as to force a priming liquid from the dialysis side to the blood side of the dialyser through the membrane, in synchrony with the induction of a multiplicity of small and repeated pressure pulses in the extracorporeal circuit, with the aim of detaching the air bubbles from the blood side of the membrane.
DE 10011208 describes a process for filling and rinsing an extracorporeal circuit in which a sterile liquid is supplied along the circuit up to an empty re-infusion container through a secondary line which branches from the arterial line. The sterile liquid, before entering the extracorporeal circuit, is filtered through the membrane of the dialyser or a sterile filter.
U.S. Pat. No. 6,331,252 is a process for priming the blood side of a dialyser having the dialysis side connected to a preparation circuit of the dialysis liquid. A measured flow of dialysis liquid is conveyed to a first pump, then to a first flow meter and then to the inlet of the dialysis side of the dialyser. A part of the flow is forced to pass through the membrane of the dialyser in order to prime the blood side, while the remaining part is conveyed to the outlet of the dialysis side of the dialyser and then to a second flow meter and to a second pump. The two pumps are commanded by flow rate signals supplied by the flowmeters so that the flow rate on the outlet of the dialysis side is lower than the flow rate at the inlet.
WO 02/098491 describes a process for filling and washing a dialyser, the dialysis side of which is filled with a physiological solution, a part of which is forced to pass through the membrane of the dialyser into the blood side and then into the extracorporeal circuit. The patient connections of the arterial and venous lines are connected to one another so as to form a closed circuit. The blood pump is of the reversible type, able to circulate the liquid in both directions. The arterial expansion chamber is connected to the outside ambient. The physiological solution which fills the extracorporeal circuit is drained through the discharge connectable to the patient connection of the arterial line.